The present application relates to electronic devices, and in particular, to electronic patches that can attach to human skin for conducting measurement.
Electronic patches can be used for tracking objects and for performing functions such as producing sound, light or vibrations, and so on. As applications and human needs become more sophisticated and complex, electronic patches are required to perform a rapidly increasing number of tasks. Electronic patches are often required to be conformal to curved surfaces, which in the case of human body, can vary overtime.
Electronic patches can communicate with smart phones and other devices using WiFi, Bluetooth, Near Field Communication (NFC), and other wireless technologies. NFC is a wireless communication standard that enables two devices to quickly establish communication within a short range around radio frequency of 13.56 MHz. NFC is more secure than other wireless technologies such as Bluetooth and Wi-Fi because NFC requires two devices in close proximity (e.g. less than 10 cm). NFC can also lower cost comparing to other wireless technologies by allowing one of the two devices to be passive (a passive NFC tag).
Bluetooth is another wireless communication standard for exchanging data over relatively longer distances (in tens of meters). It employs short wavelength UHF radio waves from 2.4 to 2.485 GHz from fixed or mobile devices. Bluetooth devices have evolved to meet the increasing demand for low-power solutions that is required for wearable electronics. Benefited from relatively longer reading distance and active communication, Bluetooth technologies allow wearable patches to continuously monitoring vital information without human interference, which is an advantage over NFC in many applications.
Wearable patch (or tag) is an electronic patch to be worn by a user. A wearable patch is required to stay on user's skin and operate for an extended period of time from hours to months. A wearable patch can contain a micro-electronic system that can be accessed using NFC, Bluetooth, WiFi, or other wireless technologies. A wearable patch can be integrated with different sensors such as vital signs monitoring, motion track, skin temperature measurements, and ECG detection.
Despite recent development efforts, current wearable patches still suffer several drawbacks: they may not provide adequate comfort for users to wear them; they may not stay attached to user's body for the required length of time; and they are usually not aesthetically appealing. The conventional wearable patches also include rigid polymer substrates that are not very breathable. The build-up of sweat and moisture can cause discomfort and irritation to the skin, especially after wearing it for an extended period of time.
Conventional wearable thermometer patches have the additional challenge of inaccurate temperature measurement due to factors such as thermal resistance between the temperature sensor and the human skin, conduction loss of the temperature sensor to the ambient environment, as well as temperature reduction in the user skin caused by the thermal conduction to the wearable patch. Moreover, conventional wearable thermometer patches can also have slow measurement responses.
Another challenge for conventional wearable thermometer patches is that the user's skin may interfere with their proper wireless communications. For example, the antenna's communication range can be significantly reduced by the adjacency to user's skin. The wireless communication range of an antenna in contact with the skin is less than half the range for an antenna that is placed 4 mm away from the user's skin.
Another challenge is that it is extremely difficult to measure the surface temperature accurately, especially when measuring the human skin temperature which being impacted by the blood circulation under the skin. Several critical factors can impact the continuous measurement of armpit temperature: the ambient temperature can impact temperature measurement when arm is opened; and thermal contact resistance can change when the contact between the temperature probe and human skin became loose.
There is therefore a need for a flexible wearable electronic patch that can correctly measure temperatures of user's skin with high accuracy and fast response time, while capable of performing wireless communications in a required range.